The present invention relates in general to a system for temporarily shoring the walls of excavation holes which can be easily and quickly installed and removed.
There are many times on construction projects when a hole needs to be excavated to make room for new underground facilities, such as underground storage tanks, etc. The vast majority of the time safety regulations issued by groups, such as OSHA (Occupational Safety and Health Authority), require that excavated holes be shored to prevent their sides from caving in. Upon completion of work within the excavation, the shoring is either removed or abandoned in place. Since the new facility usually supports the permanent earth pressure, the shoring therefore only serves a temporary purpose during construction.
Obviously, to meet OSHA regulations, any shoring must be properly designed and constructed. There are two principle known shoring methods which are considered sufficient to meet OSHA standards. The first of these methods is illustrated in FIGS. 1A and 1B and employs a plurality of vertically disposed steel sheet piles 10 which are connected to one another using ball and socket interconnects as illustrated at 12. As illustrated, the steel sheet piles are typically Z-shaped steel pieces and are driven into the ground before a hole 16 is excavated. An impact or vibratory type hammer is employed for this purpose, and each of the sheets must be driven down incrementally until they are fully in the ground. A typical hole requires many pieces of the sheet piles 10, and the installation process is very slow. In addition, for deep holes, a plurality of horizontal reinforcing members 24, otherwise known as walers, must be attached to the steel sheet piles 10 on the hole facing sides thereof to provide addition support to resist the earth pressure.
The sheet pile shoring method illustrated in FIGS. 1A and 1B is normally used where extremely soft or runny soils are encountered, or where the ground water level is very high. Although sheet piles are not water tight, they do help diminish the flow of water into the excavation. However, sheet piles are very difficult or even impossible to install in dense soils. Further, they are expensive and time consuming to install when used as temporary shoring and are normally extracted upon completion of the underground construction due to the relatively high material cost. This shoring method is actually best suited for permanent shoring, such as in bulk heads along waterfront areas.
A second known shoring method is illustrated in FIGS. 2A and 2B. In this method, a plurality of vertical steel I-beams 20, otherwise known as soldier piles, are installed into the ground in a spaced manner around the perimeter of a hole 22 to be shored. Typically, the soldier piles 20 are spaced about six to eight feet on center and are either driven into the ground or set into pre-drilled holes. As the hole 22 is excavated, a plurality of three to four inch thick wood timbers 24, otherwise known as lagging, is placed behind the front flanges 26 of the I-beams 20, and holds the soil in place between the I-beams 20. As with the sheet pile method, walers 28 and/or bracing are commonly used to provide additional support of the earth pressure behind the soldier piles 20.
The soldier pile and lagging method is normally used in competent soils which allow a minor temporary undercut to facilitate lagging placement. The piles can be pre-drilled to eliminate vibration or noise concerns in many cases. Further, they can penetrate very dense soils where sheet piles cannot, although they are not used in very soft or runny soils or in high ground water conditions.
Due to the relatively low cost of materials involved with this method, the soldier piles and wood lagging are preferably abandoned in place once the construction project is finished. However, the process of pre-digging to place lagging usually results in voids behind the lagging. Further, the lagging is installed with spacer blocks to prohibit buildup of water pressure against the shoring, and this allows for loss of soil between the lagging. There is also concern that as the timber lagging decomposes over time, a void will be left in its place. It is therefore very common to have minor settlement of the ground around abandoned lagging and as a result, many areas prohibit leaving lagging in the ground. Unfortunately, the subsequent removal of the lagging upon completion of the underground construction is extremely difficult, costly and dangerous.
In view of the above drawbacks of conventional hole shoring techniques, and as OSHA and other safety related groups continue to increase both enforcement of hole shoring safety standards and fines for violation of the standards, a great need has developed for an improved shoring system which eliminates the drawbacks of the two previously discussed shoring methods.